Comments on: Isolated laptop power supply issues

By: Shauna | Financial Advisor Brisbane

Shauna | Financial Advisor Brisbane — Tue, 03 Feb 2026 08:17:41 +0000

Interesting read nice breakdown of how isolation (or lack of it) in laptop power supplies can cause noise and safety issues. Clear reminder that PSU design really matters.

By: Christophe DEMION

Christophe DEMION — Wed, 18 Oct 2023 10:32:30 +0000

I fixed the problem by replacing the power code to the psu with a hp power cord that has ground connected. No longer any tingling sensation and all devices connected perfectly isolated and protected.

By: Tomi Engdahl

Tomi Engdahl — Sun, 06 Aug 2023 14:47:57 +0000

The secondary side should be completely floating. The problem is that there is also a small and secondary receptacle within the transformation, so that the branding frequency – usually a few hundred kilos – moves to the secondary as Common Mode and causes the supplier not to meet the EMC requirements.
To solve this problem, add the cap (which connects the secondary to the quiet side of the initial). It is actually an exploitation of a small “leakage” device between the initial and secondary to solve the EMC problem.

By: Tomi Engdahl

Tomi Engdahl — Sun, 06 Aug 2023 14:47:31 +0000

capacitor from mains side to low voltage side in ungrounded power supplies more norm than design blunder. It is generally needed for the power supply to meet all EMC regulations. The design should also meet safety regulations, so the capacitance value needs to be low enough and the capacitor needs to meet “safety capacitor” specifications for this type of application. There will be more or less leakage through this capacitor depending on which way the adapter is plugged in (does capacitor “hot: end get connected to live or neutral).

By: Tomi Engdahl

Tomi Engdahl — Mon, 18 May 2020 06:11:38 +0000

Sujit Gupta this looks isolated, but it still has capacitor between mains side low voltage side.
“To suppress the high frequency common mode is is necessary to put capacitors between the input and output side of the power supply with a capacitance substantially higher than the capacitance in the flyback transformer.”
“When desinging a class 2 (unearthed) PSU we have no choice but to connect these capacitors to the input “live” and/or “neutral”. Since most of the world doesn’t enforce polarity on unearthed sockets we have to assume that either or both of the “live” and “neutral” terminals may be at a sinificant voltage relative to earth”
“That means on a class 2 PSU we have a difficult tradeoff between safety and EMC. Making the capacitors bigger improves EMC but also results in higher “touch current” (the current that will flow through someone or something who touches the output of the PSU and mains earth).”
https://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do

By: Tomi Engdahl

Tomi Engdahl — Mon, 03 Nov 2014 13:22:31 +0000

Fixing Faulty But Genuine Apple Power Adapters
http://hackaday.com/2014/11/01/fixing-faulty-but-genuine-apple-power-adapters/

Being a miracle of modern manufacturing doesn’t mean Apple gets it right all the time; the UK adapter doesn’t use the ground plug, leading to the power supplies singing at 50 Hz when plugged in. [Gareth] had had enough of the poor design of his charger and decided to fix it.

Solving 50Hz buzz/vibration/shock on Macbooks.
http://garethhayes.net/apple-power-plug-not-earthed/

Apple has definitely dropped the ball, almost everyone I know with a Macbook complains about the “buzzing” or “vibration” and even the occasional “pinching” or electric shock. I’m not sure how this happened, considering how well built and thought out their products are in general.

Apple AC/DC adapters are meant to be internally earthed (isolated/floating output), but they also come with an earth connection and in many of the interchangeable plugs that come with Macbooks this is connected and there’s no buzzing issue.

I verified what this was by using a multimeter to measure the frequency from the case to the ground, and it is indeed 50Hz. While this is not necessarily due to a lack of earthing per se (in theory these power supplies don’t need to be earthed), if the adapter is earthed the problem disappears, which is better than being shocked all the time.

You could play it safe by always using the longer power cable

This mod will ground the Macbook, and current will no longer use your body for grounding.

By: Ilya

Ilya — Thu, 23 Jan 2014 18:33:50 +0000

There is a real problem with my new MacBook Pro – touch current. I’m going to tear-off that capacitor. Don’t care about EMI specs.

By: Dianne

Dianne — Thu, 23 Jan 2014 01:02:54 +0000

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By: Lona

Lona — Wed, 22 Jan 2014 21:40:27 +0000

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In todays society that is hard to achieve. I am grateful, Imogene

By: Rona Warbritton

Rona Warbritton — Sun, 01 Dec 2013 00:03:37 +0000

It’s strange that every macbook has different charger.